Increase in Hydrophobicity of Signal Peptide Enhances Secretion of Penicillin G Acylase.

An artificial strong hydrophobic signal peptide (ASP), containing ten leucines in tandem in the hydrophobic core, was utilized to replace the wild type signal peptide (WTSP) of penicillin G acylase (PAC), by the fusion to its 4 pro site. PAC expression plasmids, including pKKpacdeltaSP, pKKpacWTSP, pKKpacASP, pETpacWTSP and pETpacASP, were constructed. The length and the amino- and carboxyl-terminus amino acid composition of ASP and WTSP were kept identical. The activity assay and Western-blotting analysis were used to study the effect of ASP and WTSP on the secretion of PAC in tac, T7 and dissolved-oxygen regulation expression systems, respectively. Lack of signal peptide in pKKpacdeltaSP resulted in the accumulation of 91 kD PAC precursor (without signal peptide, but with the space peptide between alpha-subunit and beta-subunit) in the cytosol, indicating that the secretion of PAC depends on the signal peptide. In BL21(pKKpacASP) cells, the PAC activity and proprecursor (with signal peptide and space peptide) processing capacity were increased by about 54% and 38.5%, respectively, in comparison with BL21(pKKpacWTSP) cells. Compared with BL21(DE3) (pETpacWTSP), however, the PAC activity and proprecursor processing capacity in BL21(DE3) (pETpacASP) were enhanced by about 69% and 43.5%, respectively. The PAC activity expressed from pETpacASP was about 67% more than that from pETpacWTSP in the dissolved-oxygen-regulated expression system GJ100. Resulting from the strong hydrophobicity of ASP, therefore, the PAC activity and proprecursor processing capacity were increased by about 63% and 41% on average, respectively, in comparison with WTSP. In conclusion, the increase in hydrophobicity of the signal peptide hydrophobic core enhanced the secretion of penicillin G acylase.